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I was wondering if it would be possible to use a custom attribute in C# on a property that has some items.

For instance, I have a List with a default initialization of some items of type T and I want to check through an attribute if List has only unique items. I know that a List can have multiple similar objects in it, therefore you should use a HashSet to make sure only unique items exist. However, I can still declare some duplicate items in this HashSet at compile time and I would not receive any errors... (I want to receive errors before I run the program) So I was wondering if I could use something like:

[HasUniqueItemsAttribute]
public IList<string> MyCollection { get; set; } = new List<string>()
{
     "example 1",
     "example 2",
     "example 1"
};

Then I would receive an error on MyCollection that indicates that this default initialized collection does not contain unqiue items... Does anyone know how to do this?

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  • In principle, that should work. Although it would only make sense for initialization where the collection item types are well-known. I think what you are looking for is a custom analyzer: learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/tutorials/… But that's a lot of work to guard against something that should be easy to check yourself. Commented Nov 5, 2022 at 22:18
  • If you want to ensure uniqueness then you shouldn't be using List<T>, try HashSet<T> instead. Commented Nov 5, 2022 at 22:42
  • @Leandro your suggestion looks very interesting. I'll definitely look into it. Commented Nov 5, 2022 at 23:08
  • @DavidG You are probably right. Now that I think about it, a HashSet by default removes all duplicates. So even though I initialize a hashset with duplicate values, the hashset will remove them. I was just wondering a way for this, when using a List. Commented Nov 5, 2022 at 23:09
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